This invention relates to a vehicle mounted generator having an improved cooling system.
FIG. 1 shows an example of a conventional generator having a cooling system including a cooling fan, in which reference numerals 1, 2, 3, 3a, 3b, 3c and 3d depict a pulley, a rotor shaft coupled to the pulley, a rotor fixedly secured to the rotor shaft, teeth portions A, teeth portions B, a ring of a nonmagnetic material and a rotor core, respectively. A front bracket 4 and a rear bracket 5 rotatably support the shaft 2 via bearings 6 and 7. An exciting coil 8 is wound on a core 9 fixed to the rear bracket 5. A stator coil 10 is fixedly supported between the front and the rear brackets, and mounts a stator coil 10a. Reference numerals 11, 12 and 13 depict a rectifier, a voltage regulator and a fan, respectively, and the fan is fixed to the shaft 2 so that it can rotate therewith. The rear bracket 5 is formed with cooling air suction holes 14 in its side wall and the front bracket 4 is formed with cooling air discharge holes 15 in its side wall.
In operation, the pulley 1 is driven by a belt (not shown) of a vehicle engine (not shown). Therefore, the rotor shaft 2 and hence the rotor 3 fixedly secured thereto are rotated. The teeth portions 3a and 3b are induction members alternately magnetized in opposite polarities by the exciting coil 8, and are interleaved with each other so that when the rotor 3 rotates along the inner periphery of the stator core 10, an electromotive force is induced in the stator coil 10a. Since the electromotive force is alternating, it is rectified by the rectifier 11 and supplied to a battery and/or other electrical loads. The voltage regulator 12 functions to control the exciting current in the coil 8 so that the electromotive force induced in the stator coil 10a is maintained constant. When the fan 13 is rotated together with the pulley 1, air is drawn through the suction holes 14 to the interior of the brackets to cool the rectifier 11, the voltage regulator 12, the exciting coil 8, the stator core 10 and the stator coil 10a, etc., and then exits through the discharge holes 15.
It is generally understood that the cooling capacity of the fan of such a conventional generator mentioned is not sufficient. Therefore, it is impossible to increase the output current thereof due to increased temperature when the engine rotates at a low speed with a reduced amount of cooling air. Further, since the temperature of the air introduced through the suction holes 14 is usually high because it passes along the hot engine, it may increase the temperature of the electrical components, causing the output current to be reduced and requiring the use of some expensive materials for providing heat resistivity to these components.
In order to resolve this problem, it may be possible to make the size of the fan larger to thereby increase the flow rate of cooling air. This approach, however, produces other problems such as noise and the difficulty of mounting such a large fan on the generator.
In order to resolve all of the above mentioned problems, U.S. Pat. No. 4,295,067 proposes the use of a heat pipe instead of the fan. As is clearly shown in this U.S. Patent, the heat pipe is provided outside the brackets and adapted to cool components of the generator which generate large quantities of heat. The cooling efficiency of such a system is satisfactory. However, due to the use of the heat pipe arranged outside the brackets, the size of the generator becomes very large, necessarily causing a problem in mounting the generator in a limited space.